Using a pseudopotential plane-waves method,we calculate the phonon dispersion curves,thermodynamic properties,and hardness values of α-CdP;and β-CdP;under high pressure.From the studies of the phonon property and en...Using a pseudopotential plane-waves method,we calculate the phonon dispersion curves,thermodynamic properties,and hardness values of α-CdP;and β-CdP;under high pressure.From the studies of the phonon property and enthalpy difference curves,we discuss a phase transform from β-CdP;to a-CdP;in a pressure range between 20 GPa and 25 GPa.Then,the thermodynamic properties,Debye temperatures,and heat capacities are investigated at high pressures.What is more,we employ a semiempirical method to evaluate the pressure effects on the hardness for these two crystals.The results show that the hardness values of both α-CdP;and β-CdP;increase as pressure is increased.The influence mechanism of the pressure effect on the hardness of CdP;is also briefly discussed.展开更多
The structural, dielectric, lattice dynamical and thermodynamic properties of zinc-blende CdX （X=S, Se, Te） are studied by using a plane-wave pseudopotential method within the density-functional theory. Our calculat...The structural, dielectric, lattice dynamical and thermodynamic properties of zinc-blende CdX （X=S, Se, Te） are studied by using a plane-wave pseudopotential method within the density-functional theory. Our calculated lattice constants and bulk modulus are compared with the pubfished experimental and theoretical data. In addition, the Born effective charges, electronic dielectric tensors, phonon frequencies, and longitudinal opticaltransverse optical splitting are calculated by the linear-response approach. Some of the characteristics of the phonon-dispersion curves for zinc-blende CdX （X= S, Se, Te） are summarized. What is more, based on the lattice dynamical properties, we investigate the thermodynamic properties of CdX （X= S, Se, Te） and analyze the temperature dependences of the Helmholtz free energy F, the internal energy E, the entropy S and the constant-volume specific heat Cv. The results show that the heat capacities for CdTe, CdSe, and CdS approach approximately to the Petit-Dulong limit 6R.展开更多
Using the linear-response method, we investigate the phonon properties of β-cristobalite crystal under electronic ex- citation effect. We find that the transverse-acoustic phonon frequency becomes imaginary as the el...Using the linear-response method, we investigate the phonon properties of β-cristobalite crystal under electronic ex- citation effect. We find that the transverse-acoustic phonon frequency becomes imaginary as the electron temperature is increased, which means that the lattice of β-cristobalite becomes unstable under intense laser irradiation. In addition, for the optic phonon mode, the LO（H）-TO（H） splitting disappears when the electronic temperature reaches a certain value, corresponding to the whole transverse-acoustic phonon branches becoming negative. It means that the electronic excitation destroys the macroscopic electric field of β-cristobalite. Based on the calculated phonon band structures, some thermo- dynamic properties are calculated as a function of temperature at different electronic temperatures. These investigations provide evidence that non-thermal melting takes place during a femtosecond pulse laser interaction with β-cristobalite.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.11547158)the Doctoral Fund of Zhengzhou University of Light Industry,China(Grant Nos.2014BSJJ088 and 2015XJJZ022)
文摘Using a pseudopotential plane-waves method,we calculate the phonon dispersion curves,thermodynamic properties,and hardness values of α-CdP;and β-CdP;under high pressure.From the studies of the phonon property and enthalpy difference curves,we discuss a phase transform from β-CdP;to a-CdP;in a pressure range between 20 GPa and 25 GPa.Then,the thermodynamic properties,Debye temperatures,and heat capacities are investigated at high pressures.What is more,we employ a semiempirical method to evaluate the pressure effects on the hardness for these two crystals.The results show that the hardness values of both α-CdP;and β-CdP;increase as pressure is increased.The influence mechanism of the pressure effect on the hardness of CdP;is also briefly discussed.
基金Supported by the National Natural Science Foundation of China under Grant No 11374217
文摘The structural, dielectric, lattice dynamical and thermodynamic properties of zinc-blende CdX （X=S, Se, Te） are studied by using a plane-wave pseudopotential method within the density-functional theory. Our calculated lattice constants and bulk modulus are compared with the pubfished experimental and theoretical data. In addition, the Born effective charges, electronic dielectric tensors, phonon frequencies, and longitudinal opticaltransverse optical splitting are calculated by the linear-response approach. Some of the characteristics of the phonon-dispersion curves for zinc-blende CdX （X= S, Se, Te） are summarized. What is more, based on the lattice dynamical properties, we investigate the thermodynamic properties of CdX （X= S, Se, Te） and analyze the temperature dependences of the Helmholtz free energy F, the internal energy E, the entropy S and the constant-volume specific heat Cv. The results show that the heat capacities for CdTe, CdSe, and CdS approach approximately to the Petit-Dulong limit 6R.
基金support by the National Natural Science Foundation of China(Grant Nos.11374217 and 11547158)
文摘Using the linear-response method, we investigate the phonon properties of β-cristobalite crystal under electronic ex- citation effect. We find that the transverse-acoustic phonon frequency becomes imaginary as the electron temperature is increased, which means that the lattice of β-cristobalite becomes unstable under intense laser irradiation. In addition, for the optic phonon mode, the LO（H）-TO（H） splitting disappears when the electronic temperature reaches a certain value, corresponding to the whole transverse-acoustic phonon branches becoming negative. It means that the electronic excitation destroys the macroscopic electric field of β-cristobalite. Based on the calculated phonon band structures, some thermo- dynamic properties are calculated as a function of temperature at different electronic temperatures. These investigations provide evidence that non-thermal melting takes place during a femtosecond pulse laser interaction with β-cristobalite.
